Joe meek sound compressor scratch project blowing up 12V AC

Need help with a project? Trying to find a component? Post any general technical questions here.
Post Reply
Posts: 1
Joined: Mon Oct 24, 2016 12:08 pm

Joe meek sound compressor scratch project blowing up 12V AC

Post by nikkum » Mon Oct 24, 2016 12:31 pm

My son is actually an Architecture student but heavily into music too. He and I have been buiding a Joe Meek compressor from scratch. PCB made using blue transparency sheet from Maplins and some ferric Chloride etc. Board looked perfect and all copper lines checked fine. Inserted all components. Son may have made the mistake of not putting cradles on ICs (?burned the ICs?). Resistors/Diodes tested and fine. I am buying a capacitance tester as my multimeter doesnt check this and will take all the capacitors off and test them.
Presently we have built board and on inserting the 12 AC AC 1amp adapter the "on" LED does not light and after a few minutes the adapter burns out and no further current sent from adapter (£13!)
I obviously need to check the polarity (some are "film and ?dont have polarity?) and function of the capacitors and will remove them from the board to do this. I think we also need to take off the ICs and get new ones with cradles to avoid burning them up with solder heat.
If this doesnt work what would be the next step?
I keep telling my son this is science not Harry Potter wizardry and applying patience and logic should sort it out but we need a little bit of kind support!
Many thanks for anything the Forum can offer. We are not giving up!
(is burning out of the adapter consistent with dud or reversed polarity capacitor?)
Regards to all
The overview of the project with included links to PCB plans etc
(187.36 KiB) Downloaded 292 times

Posts: 217
Joined: Sun Oct 04, 2015 6:18 pm

Re: Joe meek sound compressor scratch project blowing up 12V

Post by David » Wed Oct 26, 2016 5:44 pm

It is difficult to trouble shoot from a distance, but the burning out of the AC adapter would indicate a heavy overload, probably caused by a short circuit. Some things to look out for:
1. The most likely way to get a short circuit is by an accidental solder bridge between adjacent tracks, or adjacent pins on the ICs.
2. Look for ICs inserted the wrong way round (very easy to do this!) - did you notice any getting hot before the adapter burnt out?
3. Components like diodes, transistors and electrolytic capacitors do not take kindly to reversed polarity. Reversed electrolytics can short (I remember being in a lab when a large one blew up like a bomb - tiny flakes of aluminium floated down like snow!) Make sure that they all have been inserted correctly - the layout diagram should indicate the polarity of each. Low value capacitors and fixed resistors are not polarised and can be inserted either way round.

Hope this helps

Post Reply